Authorities had hoped the dolphin could escape on its own during high tide, but were prepared to put divers in to help if needed.

“We did just get confirmation that it did not make it,” said Joanne Biegert, a spokeswoman for the Riverhead Foundation for Marine Research and Preservation, a rescue group in New York.

According to video shot at the scene, the dolphin appeared to be about 7 feet long. It periodically surfaced and appeared to be trying to snort away a dark material.

In 2007, a baby minke whale -- immediately nicknamed Sludgie -- was trapped in the narrow canal. It died before it could be coaxed to leave.

The area was once known for its factories and is generally regarded as one of the more polluted parts of the city. In 2010, it was named a federal Superfund site by the Environmental Protection Agency.